1. Field of the Invention
The present invention relates to a ceramic shaped article based on dense, non-metallic, mechanically resistant materials, such as, for example, high-melting metal carbides, metal nitrides, metal borides and metal oxides, especially aluminum oxide and zirconium oxide.
2. Description of the Prior Art
Ceramic shaped articles of sintered materials have already found usage in wide areas of industrial technology. They are used especially where a high degree of hardness, good resistance to wear and good temperature resistance are required. Further broadening of the use of these materials is limited, however, because they have too low a bending strength for many fields of application, and an inadequate fracture toughness, expressed as K.sub.Ic -value.
Numerous attempts to improve the mechanical strength of sintered ceramic shaped articles have been made. Thus, DE-OS No. 25 49 652 discloses the intercalation of materials existing at room temperature and combustion temperature in various enantiotropic solid modifications. On cooling the shaped articles after the combustion process, microfissures form which are capable of absorbing forces acting upon the shaped article by means of subcritical growth.
According to a more recent proposal by the present inventors and disclosed in DE-OS No. 27 44 700, a sintered material contains zirconium oxide and/or hafnium oxide in metastable tetragonal modification at room temperature (corresponding to U.S. Pat. No. 4,218,253) Stress acting on a shaped article produced from such a sintered material results in conversion of the metastable tetragonal modification into the monoclinic modification with consequent absorption of the applied stress.
In the past, it has been found that neither the storing of relatively coarse particles and the resulting generation of microcracks according to German DE-OS No. 25 49 652 (Claussen) nor the storing of ZrO.sub.2 particles present in the metastable tetragonal modification in the range of 0.05 to 2 .mu.m (Dworak) are sufficient in each case. On the contrary, it has been found that an extremely uniform structure with a very small particle size must be present in order to obtain especially good material characteristics.